Second-Generation Locking Mechanisms and Ethylene Oxide Sterilization Reduce Tibial Insert Backside Damage in Total Knee Arthroplasty

This study evaluated the effects of polyethylene quality and locking mechanism on damage to the nonarticulating (backside) surface of retrieved tibial inserts in total knee arthroplasty. Inserts with peripheral capture (PC) locking mechanisms and ethylene oxide (EtO)-sterilized polyethylene were hypothesized to prevent major backside damage. A total of 156 inserts were sorted by locking mechanism and sterilization method and analyzed by damage scoring methods. Ninety-seven specimens exhibited burnishing. Significant positive linear correlations were observed between damage score and age in vivo for all combinations, but damage occurred at a significantly lower rate for second-generation PC implants with EtO sterilization. Most specimens in this group were undamaged (46/72), with others exhibiting only burnishing. Sex, body mass index, and weight did not influence backside damage.     

In Vivo Oxidation Contributes to Delamination but not Pitting in Polyethylene Components for Total Knee Arthroplasty

The aim of this study was to better understand how in vivo oxidation contributes to fatigue damage in total knee arthroplasty (TKA). A total of 119 tibial inserts were consecutively collected after revision surgery. Of the 119 polyethylene retrievals, 29 were gamma sterilized in air (historical), whereas the remaining 90 were gamma sterilized in nitrogen (conventional). Surface damage assessment and characterization of oxidation were performed on all the retrievals. Delamination was significantly more prevalent and extensive in the longer-term, highly oxidized, historical tibial inserts. Pitting damage, in contrast, seemed to be equally prevalent between both retrieval groups and was not correlated with in vivo oxidation. Our findings support our hypothesis that in vivo oxidation is a contributing factor to delamination, but not pitting, in TKA. Despite the lower oxidation displayed by conventional retrievals, this study provides strong evidence that delamination secondary to in vivo oxidation may occur during the second decade of implantation.     

Unilateral tibial polyethylene liner failure in bilateral total knee arthroplasty--bilateral retrieval analysis at 8 years

This is a report of a unique case of bilateral simultaneous total knee arthroplasties in which one tibial liner failed dramatically, whereas the other liner showed minimal evidence of wear. This unique case allows isolation of component factors as the primary contributing etiology to failure. The differentiating characteristic was the method of sterilization and the shelf life of the polyethylene liner. The insert that showed minimal wear was sterilized with gamma radiation in a barrier package and had a shelf life of less than 1 year, whereas the insert that failed dramatically was sterilized in air and had a shelf life of more than 5 years. This case provides a dramatic example of the potential detrimental effects of manufacturing details on the performance of orthopedic implants, particularly polyethylene inserts.     

Ceramic versus cobalt-chrome femoral components; wear of polyethylene insert in total knee prosthesis

The present study aimed to determine the effect of femoral component materials and sterilization methods on wear properties of total knee prostheses by using a knee simulator test and retrieval analysis. The simulator test revealed that ultrahigh molecular weight polyethylene (UHMWPE) inserts had remarkably lower wear against the ceramic femoral component than against the Co-Cr femoral component. However, the retrieval study revealed no significant difference in the linear wear between the former and the latter. The alumina ceramic/UHMWPE insert combination showed a mild wear. However, whether cross-linking by gamma-ray sterilization reduces wear remained unconfirmed. In contrast, oxidative degradation and/or delamination was confirmed. Thus, we conclude that alumina ceramic/ethylene oxide gas-sterilized UHMWPE insert in a total knee prosthesis might exhibit a good wear resistance.     

Post damage in contemporary posterior-stabilized tibial inserts: influence of implant design and clinical relevance

The mechanisms of damage at the polyethylene post in 3 contemporary tibial insert designs were evaluated and compared with a historical standard (Insall-Burstein II; Zimmer, Warsaw, Ind). One hundred five gamma sterilized posterior-stabilized tibial inserts were revised after an average of 4.7 years (0.05-13.6 years). Retrievals were classified according to their designs: Insall-Burstein II (n = 28); PFC (Johnson & Johnson, Raynham, Mass; n = 30); NexGen (Zimmer; n = 32); and Scorpio (Stryker Orthopaedics, Mahwah, NJ; n = 15). Reasons for revision and patient details were available. Surface damage scoring and photogrammetry were performed on all the retrieved tibial inserts. Oxidation analysis was carried out for traceable historical, gamma air-sterilized and conventional, gamma inert-sterilized tibial inserts (n = 61) with the use of infrared spectroscopy. The posts for all 3 contemporary designs exhibited damage similar to the historical controls. Articular, post, and backside damage scores significantly increased with implantation time. Post damage was insensitive to design and patient factors but was exacerbated by oxidation. An association between damage at the post and articular surface was also confirmed. Logistic models suggested an interaction between post damage, backside surface damage, and implant loosening.     

Wear,delamination, and fatigue resistance of melt‐annealed highly crosslinked UHMWPE cruciate‐retaining knee inserts under activities of daily living

The wear, delamination, and fatigue resistance of artificially aged gamma irradiation‐sterilized conventional polyethylene (CPE) and gas‐plasma‐sterilized melt‐annealed highly crosslinked polyethylene tibial inserts (HXPE) were compared. Six CPE and 12 HXPE (six irradiated at 58 kGy and six at 72 kGy) left knee inserts were wear tested for 5.5 million cycles (Mc) under loads and motions that mimic activities of daily living, such as walking, chair rise, stair ascent, and deep squatting. Another six HXPE (72 kGy) and six CPE inserts were also tested under conditions that could produce severe delamination for 8 Mc. Ten other knees (five 72 kGy HXPE and five CPE) were subjected to posterior edge loading fatigue testing for 5 Mc. The HXPE inserts had an average wear rate reduction of about 80% relative to their CPE counterparts during all activities. All of the CPE inserts delaminated and fractured during high cycle deep squat (152° flexion) motions, while all the HXPE remained intact. None of the HXPE inserts delaminated after 8 Mc, while all of the CPE inserts developed delamination damage within 1.5–5.8 Mc of delamination testing. All CPE inserts developed subsurface cracks and delamination within 2.8 Mc during posterior edge loading fatigue studies, while none of the HXPE inserts showed cracking or delamination after 5 Mc. These results show that aged HXPE has higher wear and fatigue resistance than aged CPE, and offers potential long‐term advantages for young active patients with sustained activities of daily living. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:1120–1126, 2010     

聚羟基丁酸酯可吸收缝线灭菌方法的实验研究

目的：研究不同的灭菌方法对聚羟基丁酸酯（PHB）可吸收缝线的降解性和力学特性的影响。方法：将聚羟基丁酸酯（PHB）可吸收缝线进行酒精浸泡、环氧乙烷、紫外线照射三种方法进行灭菌处理后,用细菌培养检测灭菌效果,用粘度法测定聚合物分子量从而观察缝线的降解性,用拉伸试验测定缝线的力学特性。结果：①酒精浸泡灭菌组有10%检出细菌,环氧乙烷及紫外线灭菌组未检出细菌;②紫外线照射灭菌和酒精浸泡灭菌组可使缝线黏度下降并具有显著性差异,环氧乙烷对缝线黏度下降的影响没有显著性差异;③经酒精和紫外线灭菌后缝线的断裂强度降低明显,差异具有显著性,经环氧乙烷灭菌后缝线的断裂强度降低无显著性差异。经紫外线灭菌后缝线的断裂伸长率明显降低,差异具有显著性,经酒精和环氧乙烷灭菌后缝线的断裂伸长率无明显降低。结论：环氧乙烷灭菌对PHB可吸收缝线的降解性和力学特性影响较小,是PHB可吸收缝线较理想的灭菌方法。     

Chemical burns due to blood pressure cuff sterilized with ethylene oxide

This paper reports two unusual instances of ethylene oxide burns that were caused by the blood pressure cuff sterilized with ethylene oxide. It is suggested that the mechanical compression caused by the blood pressure cuff facilitated penetration of ethylene oxide residues into tissues and contributed to the degree of tissue damage.     

Backside wear of Miller-Galante I and Insall-Burstein II tibial inserts

The objective of this study was to determine if there was a difference in the amount, type, and location of backside wear in the Miller-Galante I and Insall-Burstein II PE tibial inserts. A secondary objective was to determine if backside wear damage in these two designs was a function of clinical factors (patient height, weight, gender, age, and length of time of implantation), shelf life of the PE tibial insert, and tibial component thickness. Backside wear damage was assessed on 24 Miller-Galante I and 11 Insall-Burstein II tibial inserts (implantation time, 0.5-12.4 years). For both groups combined, implantation time was positively correlated to wear damage and to PE peg height into screw holes. The Miller-Galante I group had significantly larger PE pegs than the Insall-Burstein II group. The Miller-Galante I group had significantly more burnishing and larger PE pegs posteriorly than anteriorly. There was no correlation between insert shelf life before initial surgery and backside wear. The thinner the component, the larger the total damage scores in the Miller-Galante I group. This study supports the hypothesis that backside wear of PE tibial inserts may be influenced by design and component thickness and by clinical factors.     

In vivo kinematic analysis of total knee arthroplasty with four different polyethylene designs

The femorotibial contact point on the sagittal plane was measured under weight-bearing conditions in 45 subjects with implanted and nonimplanted knees. They consisted of 11 knees with flat bearing inserts, 16 knees with shallow dished inserts, 10 knees with posterior lipped inserts, 10 knees with posterior stabilized bearing inserts, and 8 normal knees selected as controls. The average amount of anterior translation of the knee with a flat bearing insert was significantly larger than that of the other implanted knees. The average femorotibial contact point did not differ significantly among knees with shallow dished, posterior lipped, and posterior stabilized bearing inserts, but posterior stabilized knees exhibited most frequently a normal posterior movement. Based on our results, it may be safer to use more anteroposterior constrained bearing inserts in total knee arthroplasty, particularly when the posterior cruciate ligament is loose.     

Gamma irradiation and ethylene oxide in the sterilization of native reindeer bone morphogenetic protein extract.

BACKGROUND AND AIMS: For human use, it is necessary to sterilize bone morphogenetic proteins (BMPs), in order to reduce the risk of infections and associated complications. We compared the effects of ethylene oxide and gamma irradiation in the sterilization of native reindeer BMP extract with regard to bone induction in the Balb/C mouse thigh muscle pouch model. MATERIALS AND METHODS: BMP extract, sterilized with ethylene oxide gas (Steri-Vac 4XL, temperature 29 degrees C, exposure time 4 h, ethylene oxide concentration 860 mg/l), or gamma irradiation at doses of 3.15 MRad was administered in implants containing 5 or 10 mg of BMP extract with collagen carrier. Non-sterilized collagen implants served as controls. New bone formation was evaluated based on the incorporation of Ca45 and radiographically three weeks after implantation. RESULTS: The collagen was not able to induce new bone visible in radiographs. The mean Ca45 incorporation in the gamma sterilized group containing 5 mg of BMP extract was 30% (p = 0.04) and that containing 10 mg of BMP extract was 60% (p = 0.02) higher than seen in the corresponding ethylene oxide sterilized groups. The mean new bone areas were 45% higher in the gamma sterilized groups than in the corresponding ethylene oxide sterilized groups, but the differences were not significant. The mean optical density of new bone in the gamma sterilized group containing 5 mg of BMP extract was 75% (p = 0.00) and in that containing 10 mg of BMP extract was 70% (p = 0.00) higher than seen in the corresponding ethylene oxide sterilized groups. CONCLUSION: Native reindeer BMP extract is more sensitive to the effects of ethylene oxide gas sterilization than gamma irradiation. These results suggest that gamma irradiation is recommendable for the sterilization of BMP extracts.     

Analysis of polyethylene thickness of tibial components in total knee replacement

BACKGROUND: Excessive wear of the polyethylene bearing surfaces of tibial components has become an important factor in early failure of total knee arthroplasty. Inadequate thickness of the polyethylene insert is one cause of excessive wear, and various minimum thicknesses have been recommended in order to reduce contact stresses within the polyethylene. However, the true thicknesses of modular polyethylene tibial inserts typically are not stated accurately by the manufacturers in their product information. The purpose of this study was to determine whether the information about the thickness of tibial inserts supplied by the manufacturers is adequate. METHODS: Five of the thinnest available polyethylene tibial inserts from five different manufacturers were selected. The minimum thickness of each was measured with use of a Sigma electronic micrometer comparator to an accuracy of +/-0.005 mm. RESULTS: The stated thicknesses of the polyethylene tibial inserts were 8, 9, and 10 mm, values that differed markedly from the actual minimum thicknesses, which ranged from 5.5722 to 6.2048 mm (mean values). CONCLUSION: The thickness of polyethylene tibial inserts has been implicated as a potential cause of excessive wear and early failure of total knee replacements. This paper highlights the fact that the information supplied by the manufacturers is inaccurate and potentially misleading; in one case, the true thickness was much less than the recommended minimum thickness. We recommend that the minimum thickness of the tibial components as well as the combined thickness of the polyethylene insert and the metal tibial tray be specified in the product information and on the packaged insert.     

Determination of Reference Geometry for Polyethylene Tibial Insert Wear Analysis

Geometric wear analysis techniques require unworn geometries to serve as a reference in wear measurement. A method to create a reference geometrical model is described for retrieval studies when the actual unworn geometry is unavailable. Never-implanted tibial inserts were scanned with micro-computed tomography. Two, 3, or 6 insert surfaces were coaligned and averaged to create reference geometries. Individual inserts were compared with each other (manufacturing variability) and with the reference geometries (reference variability). The 3-dimensional deviations between the surfaces were recorded. The reference variability was reduced to 8.3 ± 39 μm, vs manufacturing variability of 15 ± 59 μm. Deviations were smallest on the articular surfaces where most wear occurs and were significantly less than the reported insert wear rate of 20 μm/y.     

The effect of oxidative aging on the wear performance of highly crosslinked polyethylene knee inserts under conditions of severe malalignment

First‐generation crosslinked polyethylene developed for total hip arthroplasty has not gained wide acceptance for knee arthroplasty because of the increased potential for failure under high stresses and the increased risk for oxidative damage caused by free radicals. Sequentially crosslinked polyethylene (SQXL) is a second‐generation crosslinked polyethylene that is reported to reduce the level of free radicals and preserve mechanical properties. Three groups of ultrahigh molecular weight polyethylene inserts were wear tested after artificial aging as per ASTM F2003: gamma‐irradiated in air (GA‐aged), sequentially crosslinked (SQXL‐aged), and electron‐beam irradiated and remelted (EBeam‐aged). Inserts were tested in an AMTI knee wear simulator under malalignment conditions that were two standard deviations from the mean reported for computer‐navigated and conventionally aligned techniques. GA‐aged inserts delaminated by 500,000 cycles, and were severely damaged after 1 million cycles. None of the highly crosslinked inserts (SQXL‐aged or EBeam‐aged) delaminated or showed any signs of severe wear. Mean wear rate for GA‐aged inserts was 124.6 ± 49.4 mg/million cycles. Mean wear rates for SQXL‐aged and EBeam‐aged inserts were significantly lower (1.74 ± 0.3 and 4.72 ± 0.7, respectively). These results support the low levels of free radicals and preservation of mechanical properties reported in second‐generation crosslinked ultrahigh molecular weight polyethylene. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res, 2008     

Comparison of polyethylene tibial insert damage from in vivo function and in vitro wear simulation

Function and wear of total knee arthroplasties were compared by analysis of damage patterns on polyethylene tibial inserts retrieved from patients (Group R) with inserts obtained after in vitro force‐controlled knee joint wear simulation. Two simulator input profiles were evaluated, including standard walking (Group W), and combined walking and stair descent (Group W + S), simulating varied activities and a more severe physiological environment. Damage regions on all inserts were quantitatively assessed. On average, inserts in all groups had internally rotated damage patterns and the greatest articular deformation in the lateral compartment. These patterns were more pronounced in Group W + S compared to Group W. Deformation rates of simulated inserts were analogous to about six years of physiologic function. However, both groups of simulated inserts generally underestimated the magnitude of damage area and extent observed on retrieved inserts, consistent with differences in the simulator's tibiofemoral contact mechanics and those known to occur in patients during functional activities. Modification of simulator inputs, such as the increased anteroposterior excursion and more severe loading conditions in Group W + S, can generate greater wear volume, larger damage areas, and increased surface deformation rates compared to standard inputs. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 27: 540–548, 2009     

Use of peracetic acid to sterilize human donor skin for production of acellular dermal matrices for clinical use

We previously reported methods for sterilizing human skin for clinical use. In a comparison of gamma-irradiation, glycerol, and ethylene oxide, sterilization with ethylene oxide after treatment with glycerol provided the most satisfactory dermis in terms of structure and its ability to produce reconstructed skin with many of the characteristics of normal skin. However, the use of ethylene oxide is becoming less common in the United Kingdom due to concerns about its possible genotoxicity. The aim of this study was to evaluate peracetic acid as an alternative sterilizing agent. Skin sterilized with peracetic acid was compared with skin sterilized using glycerol alone or glycerol with ethylene oxide. The effect of subsequently storing peracetic acid sterilized skin in glycerol or propylene glycol was also examined. Acellular dermal matrices were produced after removal of the epidermis and cells in the dermis, processed for histological and ultrastructural analysis, and the biological function was evaluated by reconstitution with keratinocytes and fibroblasts. Results showed that sterilized acellular matrices retained the integrity of dermal structure and major components of the basement membrane. There were no overall significant differences in the ability of these matrices to form reconstructed skin, but peracetic acid alone gave a lower histologic score than when combined with glycerol or propylene glycol. We conclude that peracetic acid sterilization followed by preservation in glycerol or propylene glycol offers a convenient alternative protocol for processing of human skin. It is suggested that this sterile acellular dermis may be suitable for clinical use.     

Oxidation,Damage Mechanisms,and Reasons for Revision of Sequentially Annealed Highly Crosslinked Polyethylene in Total Knee Arthroplasty

Background

Sequentially annealed, highly crosslinked polyethylene (HXLPE) has been used clinically in total knee arthroplasty (TKA) for over a decade. However, little is known about the revision reasons; its surface damage mechanisms; or its in vivo oxidative stability relative to conventional polyethylene. We asked whether retrieved HLXPE tibial inserts exhibited: (1) similar revision reasons; (2) improved resistance to surface damage; and (3) improved oxidative stability, when compared with conventional gamma inert sterilized polyethylene inserts.

Increase in early polyethylene wear after sterilization with ethylene oxideRadiostereometric analyses of 201 total hips

We evaluated polyethylene wear by measuring femoral head penetration in 201 THA (median age 62 (31-81) years, 117 women) extracted from 5 randomized studies aimed to assess various fixation principles. There were 30 cemented all-polyethylene Lubinus cups sterilized by gamma irradiation in a reduced oxygen environment, 65 porous-coated Trilogy cups with liners gamma-sterilized in inert gas. Moreover, 37 cemented cups were sterilized with ethylene oxide (Reflection all-poly) and 69 porous-coated cups had liners sterilized in ethylene oxide (Reflection). 28 mm femoral heads were used in all cups. The patients were followed with repeated radiostereometric measurements (RSA) up to 2 years. The activity level of the patients was evaluated by a questionnaire. After 2 years, cups with polyethylene sterilized in EtO had almost twice the proximal and 3D penetration rates, as compared with gamma-sterilized polyethylene. The penetration did not differ between the gamma-irradiated designs. Using stepwise linear regression analysis, we found that the type of sterilization, age and weight were the most important predictors and that they determined the direction of the proximal penetration rate. Activity score, male gender and proximal migration of the cup had little effect. The accelerated wear observed with the EtO-sterilized polyethylene causes concerns about long-term problems and especially in younger patients.     

Increase in early polyethylene wear after sterilization with ethylene oxide: radiostereometric analyses of 201 total hips

We evaluated polyethylene wear by measuring femoral head penetration in 201 THA (median age 62 (31-81) years, 117 women) extracted from 5 randomized studies aimed to assess various fixation principles. There were 30 cemented all-polyethylene Lubinus cups sterilized by gamma irradiation in a reduced oxygen environment, 65 porous-coated Trilogy cups with liners gamma-sterilized in inert gas. Moreover, 37 cemented cups were sterilized with ethylene oxide (Reflection all-poly) and 69 porous-coated cups had liners sterilized in ethylene oxide (Reflection). 28 mm femoral heads were used in all cups. The patients were followed with repeated radiostereometric measurements (RSA) up to 2 years. The activity level of the patients was evaluated by a questionnaire. After 2 years, cups with polyethylene sterilized in EtO had almost twice the proximal and 3D penetration rates, as compared with gamma-sterilized polyethylene. The penetration did not differ between the gamma-irradiated designs. Using stepwise linear regression analysis, we found that the type of sterilization, age and weight were the most important predictors and that they determined the direction of the proximal penetration rate. Activity score, male gender and proximal migration of the cup had little effect. The accelerated wear observed with the EtO-sterilized polyethylene causes concerns about long-term problems and especially in younger patients.     

Obstetrical analgesia in a woman allergic to ethylene oxide

A case is reported of a 28 year old woman, with untreated mitral valve disease and a professional allergy to ethylene oxide and phthalic anhydride, who presented with acute hydramnios during the 35th week of pregnancy. Emergency caesarean section having been decided on, a urinary catheter--sterilized by gamma rays and not ethylene oxide--was inserted; the gloves used had however been sterilized in ethylene oxide gas, and the patient rapidly presented with anaphylactic shock. The needles and intravenous infusion equipment used were all either sterilized in gamma rays or rinsed in large quantities of liquid. It was decided to abandon the caesarean section and attempt a vaginal delivery using morphine spinal analgesia; epidural analgesia was absolutely contraindicated because the catheters were sterilized in ethylene oxide and the patient's haemodynamic state was too precarious. Caudal anaesthesia with 0.25% bupivacaine was used to complete the spinal analgesia and speed up cervical dilation. The child was delivered with forceps and the diagnosis of oesophageal atresia was confirmed.